1. Field of the Invention
The present invention is related to planar broadband antennas and, more particularly, to an antenna with reduced edge diffraction.
2. Background Information
Antennas, such as used in Global Positioning Systems (GPS), have differing requirements depending upon the particular application for the antenna. For application to surveying activity, for example, the ideal antenna will receive only those signals originating above the horizontal plane of the antenna, and reject all other signals. Additionally, the ideal antenna will have a known and stable phase center located at the geometric center of the antenna, and have perfect circular polarization characteristics to maximize the reception of incoming right-hand polarized signals. A close approximation to such an ideal antenna can be provided by a patch antenna mounted on a choke ring ground plane. However, such a configuration is large and bulky, prohibiting its use in portable applications such as surveying.
Furthermore, many antenna radiation structures exhibit performance degradation as a result of surface wave excitation at the front surface of the antenna which produces diffractive radiation at the antenna edge. It is thus an object of the present invention to provide a slot array antenna antenna with reduced edge diffraction.
Other objects of the invention will be obvious, in part, and, in part, will become apparent when reading the detailed description to follow.
A slot-array antenna includes a nonconductive substantially planar substrate, a transmission line disposed on a rear substrate surface, and a conductive layer on the front antenna surface, the conductive layer having an array of slotted openings therein. When an electromagnetic signal is fed into one end of the transmission line and sequentially coupled into the slotted openings, a corresponding signal is emitted from the antenna substantially in the direction of the antenna axis. The front antenna surface also includes a surface wave suppression region enclosing the slotted array and a plurality of through holes disposed between the wave suppression region and the peripheral edge of the antenna to reduce diffraction of the emitted signal at the peripheral edge.